1. Field of the Invention
The present invention relates to a semiconductor wafer treating method and more particularly to a semiconductor wafer treating method used to wash a surface of the semiconductor wafer.
2. Description of the Related Art
A conventional apparatus for treating a surface of the semiconductor wafer comprises first to third treating tanks for treating the surface of the semiconductor wafer. In the first treating tank, a first mixed liquid in which HF and deionized water (DIW) are mixed is contained. In the second treating tank, deionized water (DIW) is contained. In the third treating tank, a second mixed liquid in which HCl, H.sub.2 O.sub.2, and deionized water (DIW) are mixed is contained.
In the above apparatus, firstly, the semiconductor wafer is dipped in the first treating tank for a predetermined period of time, and the surface of the wafer is treated with the first mixed liquid. This treatment is performed to remove an oxide film from the surface of the semiconductor wafer. Thereafter, the semiconductor wafer is taken out from the first treating tank. The wafer is dipped in the second treating tank for a predetermined period of time, and the surface of the wafer is washed with deionized water. Then, the semiconductor wafer is taken out from the second treating tank. The wafer is dipped in the third treating tank for a predetermined period of time, and the surface of the wafer is treated with the second mixed liquid. This treatment is used to remove Cu from the surface of the semiconductor wafer.
According to the above conventional semiconductor wafer treating method, even if the oxide film formed on the surface of the semiconductor is removed in the first treating tank, a native oxide film is formed again on the surface of the semiconductor wafer for the following three reasons.
Mover specifically, the first reason is as follows:
Since the wafer contacts air in moving the wafer into the second treating tank from the first treating tank, the native oxide film is formed again on the surface of the wafer.
The second reason is as follows;
In washing the wafer with deionized water in the second treating tank, the native oxide film is formed on the surface of the wafer by dissolved oxygen contained in the deionized water of the treating tank.
The third reason is as follows:
Since the wafer contacts air in moving the wafer into the third treating tank from the second treating tank, the native oxide film is formed on the surface of the wafer.
If the native oxide film is formed again on the surface of the semiconductor wafer, it becomes difficult to remove metal impurity material such as Cu from the surface of the semiconductor wafer by use of the second mixed liquid in the third treating tank.
FIG. 1 shows the relationship between treating time with deionized water and a rate of removing Cu from the wafer surface.
More specifically, after treating the surface of the semiconductor wafer with HF, the wafer is rinsed with deionized water whose concentration of dissolved oxygen is about 10 ppm. Cu is removed from the surface of the wafer with mixed liquid of HCl and H.sub.2 O.sub.2. The wafer is rinsed with deionized water, and dried. The relationship between rinsing time (treating time with deionized water) and the rate of removing Cu from the wafer surface is shown in FIG. 1 in the above-mentioned case. From FIG. 1, it can be understood that the rate of removing Cu from the wafer surface becomes lower as treating time with deionized water becomes lower. This is because treating time with deionized water is made longer, so that the thickness of the native oxide film, which is formed on the surface of the semiconductor again, is thickened. In other words, difficulty in removing Cu from the wafer surface is increased as the thickness of the native oxide film becomes thicker.
FIG. 2 shows the relationship between time when the wafer is left to stand in air and a rate of removing Cu from the wafer surface. In other words, the surface of the semiconductor wafer is treated with HF. Thereafter, the wafer is left to stand in air having 50% of humidity, room temperature. Then, Cu is removed from the wafer surface with mixed liquid of HCl and H.sub.2 O.sub.2. Thereafter, the wafer is rinsed by deionized water, and dried. The relationship between time when the wafer is left to stand in air and the rate of removing Cu from the wafer surface is shown in FIG. 2 in the above-mentioned case. From FIG. 2, it can be understood that the rate of removing Cu from the wafer surface becomes lower as time when the wafer is left to stand in air becomes longer. Therefore, difficulty in removing Cu from the wafer surface is increased as the thickness of the native oxide film, which is formed on the semiconductor wafer, becomes thicker.